FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES - QUANTITATIVE INFORMATION ON LEVEL 3 MEASUREMENTS (Details) - Level 3 - Forward Contract - Natural Gas $ in Thousands	Dec. 31, 2016 USD ($) $ / decatherm	Dec. 31, 2015 USD ($) $ / decatherm
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets | $	$ 1,040	$ 599
Liabilities | $	$ 114	$ 416
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward price (in dollars per dt)	3.25	1.18
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward price (in dollars per dt)	6.33	5.21
Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward price (in dollars per dt)	5.09	2.90